Gimbaled reflector antennas provide a high gain signal path over a wide field of regard extending beyond the beam width of a fixed antenna of equivalent design. This high gain signal path is provided by mechanically steering the beam to a desired location through appropriate actuation of the associated gimbals. In this fashion, a gimbaled reflector antenna may be used to track moving targets regardless of whether the antenna position itself is also changing. Gimbaled reflector antennas may also perform sequential acquisition of multiple targets at multiple positions or be used to move a fixed set of multiple beams to different locations. Thus, gimbaled reflector antennas have numerous applications in both wireless communication systems and sensor systems.
As illustrated in FIG. 1, a conventional gimbaled reflector antenna system 100 having a large field of regard requires an antenna feed 105 and a reflector 110 to remain fixed with respect to each other to minimize gain performance degradation. Because of their fixed spatial relationship, feed 105 and reflector 110 must move in tandem. Thus, to accommodate scanning of reflector antenna system 100 requires either a rotating or a flexible electrical connection 120 to carry signals to feed 105. Typical systems use rotary joints or slip rings or flexible cables with large service loops. To minimize RF front end losses, a low noise amplifier (LNA) 130 should be placed as close are possible to feed 105, often requiring it to move with the feed. The addition of LNA(s) 130, associated power supplies, and thermal control features introduce extra gimbaled mass that complicates the electrical and mechanical design of system 100.
To eliminate the complications associated with a fixed feed/reflector design, one current approach is to use what is called a “beam waveguide” that eliminates “hard” electrical connections (connection made with cables, waveguide, or other physical media such as flexible electrical connection 120) through the gimbals of a reflector system. A beam waveguide is a multiple reflector system that produces an image of the feed that is displaced from where the feed is located. This feed image orientation can be changed by rotation of one or more of the beam waveguide reflectors. This image of the feed is then used to feed a focused reflector system, producing the high gain spot pattern. Conventional beam waveguide systems require four or five reflectors in addition to two reflectors for the final focused main reflector. This large number of reflectors requires complicated design, assembly, and alignment procedures. For electrically small antenna systems, this may be impractical.
Another approach to providing large field of regard is to use a phased array antenna. Phased array antennas require small element spacing for large scan angles, resulting in a large number of elements for a given gain requirement. In addition, it difficult and expensive to produce an array that looks over a spherical field of regard of pi steradians. Moreover, the number of active electronic devices such as amplifiers and phase shifters typically make the cost prohibitive.
Accordingly, there is a need in the art for improved gimbaled reflector antenna systems that provide a large field of regard.